JP2023182999A - Fixing device - Google Patents

Abstract

To prevent wrinkles occurring in a recording material.SOLUTION: A fixing device has: a fixing belt; a suspension member that suspends the fixing belt; a pressure rotating body that applies pressure to the suspension member with the fixing belt therebetween to form a nip part, wherein the fixing belt and the pressure rotating body sandwiching and conveying a recording material carrying a toner image at the nip part and applying heat and pressure to the recording material to fix the toner image to the recording material; and a suspension roller that suspends the fixing belt on the upstream of the nip part in the direction of rotation of the fixing belt. The suspension roller is adjacent to the suspension member, and in a width direction of the suspension roller, when the center of a paper feed area of the recording material is defined as a center part and both ends of the paper feed area as both end parts, the outer diameter of the suspension roller is larger at the both end parts than the center part.SELECTED DRAWING: Figure 4

Description

The present invention relates to a fixing device that fixes a toner image to a recording material.

The image forming apparatus includes a fixing device for fixing a toner image onto a recording material. The fixing device includes a heating rotating body that applies heat necessary for fixing the toner image to the recording material, and a pressure rotating body that applies pressure to the recording material. Up to now, fixing devices using a fixing belt as a heating rotor have been proposed. Specifically, the fixing belt is rotatable and endless. A heating roller having a heat source comes into contact with the inner peripheral surface of the fixing belt to heat the fixing belt. The pressure rotating body forms a fixing nip portion together with the fixing belt. When the recording material carrying the toner image is conveyed to this fixing nip, heat and pressure are applied to the recording material, and the toner image is fixed on the recording material. A fixing device using a fixing belt has high thermal conductivity from a heat source to the surface of the fixing belt that contacts the recording material. Therefore, it is advantageous in increasing the number of sheets printed per unit time (productivity).

In a fixing device using a fixing belt, if the tension when suspending the fixing belt is not sufficient, the fixing belt may become slack. To address this issue, Japanese Patent Application Laid-Open No. 2017-83712 (Patent Document 1) proposes to apply tension to the fixing belt by arranging a suspension roller that suspends the fixing belt upstream of the fixing nip in the rotation direction of the fixing belt. giving. This suppresses slack in the fixing belt and prevents wrinkles from forming on the recording material.

JP 2017-83712 Publication

In a fixing device that uses a fixing belt and a suspended roller, there is a possibility that the conveyance speed of the recording material conveyed in the fixing nip section may differ in the width direction of the fixing belt. Specifically, in the width direction, the speed may be faster at the center of the recording material than at the edges. This difference in conveyance speed of the recording material in the width direction may cause wrinkles to occur in the recording material.

Therefore, an object of the present invention is to suppress wrinkles that occur on recording materials.

In view of the above problems, a fixing device according to the present invention includes a fixing belt that is rotatable and applies heat to a recording material, and a suspension member that comes into contact with an inner peripheral surface of the fixing belt and suspends the fixing belt. , a pressure rotating body that forms a nip portion by pressurizing the suspension member via the fixing belt, and the fixing belt and the pressure rotating body are configured to move the recording material carrying the toner image in the nip portion. The toner image is fixed on the recording material by nipping and conveying the recording material and applying heat and pressure to the recording material, and a suspension roller that suspends the fixing belt is provided upstream of the nip portion in the rotation direction of the fixing belt. The suspension roller is adjacent to the suspension member among the plurality of members suspending the fixing belt, and has a center portion of the recording material passing area in the width direction of the suspension roller. Both ends of the paper area are defined as both ends, and the outer diameter of the suspension roller is larger in the range of 50 μm or more and 300 μm or less at both ends than at the center.

According to the present invention, wrinkles generated on a recording material can be suppressed.

Schematic diagram of image forming device Schematic cross-sectional diagram of the fixing device in Example 1 Schematic cross-sectional diagram of the fixing device in Example 2 An explanatory diagram of the outer diameter of the suspended roller in this example Diagram explaining the paper wrinkle generation mechanism in this example An explanatory diagram of the paper wrinkle generation part in this example Schematic diagram of wrinkle prevention effect in this example Comparison table of effects in this example Diagram showing the relationship between position and tension due to the concave shape of the suspended roller in this example Comparison images of paper shape simulation before and after the fixing nip under the conditions of the conventional example and the example in this example

Hereinafter, an embodiment of an image forming apparatus according to this embodiment will be described based on the drawings. In the following, an example in which the present embodiment is applied to an electrophotographic full-color image forming apparatus having a plurality of photosensitive drums will be described, but the present embodiment is not limited to this, and can be applied to image forming apparatuses of various types, It can also be applied to monochrome image forming devices.

<Example 1>
<Image forming device>
A schematic configuration of the image forming apparatus of this embodiment will be described using FIG. 1.

FIG. 1 is a diagram showing a full-color image forming apparatus according to this embodiment. The image forming apparatus 1 includes an image reading section 2 and an image forming apparatus main body 3. The image reading unit 2 reads a document placed on a document table glass 21. Light emitted from a light source 22 is reflected by the document, and an image is formed on a CCD sensor 24 via an optical system member 23 such as a lens. be done. By scanning in the direction of the arrow, such an optical system unit converts the original into an electric signal data string for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and a control section 30 performs image processing in accordance with each image forming section, which will be described later. The control unit 30 also receives external input from an external host device such as a print server as an image signal.

The image forming apparatus main body 3 includes a plurality of image forming sections Pa, Pb, Pc, and Pd, and each image forming section forms an image based on the above-mentioned image signal. That is, the image signal is converted by the control section 30 into a laser beam subjected to PWM (pulse width modulation control). In FIG. 1, 31 is a polygon scanner serving as an exposure device, which scans with a laser beam according to an image signal. Then, a laser beam is irradiated onto the photosensitive drums 200a to 200d, which serve as image carriers of each of the image forming units Pa to Pd. Note that Pa is a yellow (Y) image forming section, Pb is a magenta (M) image forming section, Pc is a cyan (C) image forming section, and Pd is a black (Bk) image forming section, which correspond to each other. Form a color image. Since the image forming sections Pa to Pd are substantially the same, the details of the yellow image forming section Pa will be explained below, and the explanation of the other image forming sections will be omitted. In the Y image forming section Pa, a photosensitive drum 200a forms a toner image on its surface based on an image signal, as described below.

A primary charger 201a charges the surface of the photosensitive drum 200a to a predetermined potential. A laser beam from the exposure section 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which is charged to a predetermined potential. A developing device 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. Reference numeral 203a denotes a transfer roller that generates discharge from the back surface of the intermediate transfer belt 204 and applies a primary transfer bias having a polarity opposite to that of the toner to the intermediate transfer belt 204. Then, the toner image on the photosensitive drum 200a is transferred onto the intermediate transfer belt 204. After the transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

Further, the toner image on the intermediate transfer belt 204 is conveyed to the next image forming section, and the toner images of each color formed at each image forming section are sequentially transferred in the order of Y, M, C, and Bk. A colored image is formed on the surface. The toner image that has passed through the Bk image forming section is subjected to a secondary transfer electric field having a polarity opposite to that of the toner image on the intermediate transfer belt 204 in a secondary transfer section composed of a pair of secondary transfer rollers 205 and 206. As a result, the image is secondarily transferred onto the paper P. The paper fed from the paper feed cassette 8 or 9 waits at the register section 208, and then is transported from the register section 8 or 9 so that the toner image on the intermediate transfer belt 204 matches the position of the paper. Ru. Thereafter, the toner image on the paper is fixed onto the paper by a fixing device F serving as an image heating device. After passing through the fixing device, the paper is ejected outside the machine. In the case of a double-sided job, when the transfer and fixing of the toner on the first side (first side) of image formation is completed, the paper is turned upside down through a reversing section provided inside the image forming apparatus after fixing. Thereafter, the toner on the second side (second side) of image formation is transferred and fixed, and the sheets are discharged outside the machine and stacked on the sheet discharge tray 7.

<Fusing device>
Next, the configuration of the fixing device F in this embodiment will be described using FIG. 2.

FIG. 2 shows a schematic diagram of the overall configuration of a belt heating type fixing device F according to this embodiment. In the figure, the X direction indicates the conveying direction of the recording material P (not shown in the figure), the Y direction indicates the paper width direction, and the Z direction indicates the pressing direction. The dotted line portion represents an enlarged cross section of the nip portion N.

The fixing device F has a fixing belt (hereinafter referred to as belt) 301 as an endless rotatable heating rotating body. Furthermore, the fixing device F includes a fixing roller 300 for supporting the fixing belt from the inside, a heating roller 307, a suspension roller 308, and a pressure rotating body that faces and presses the fixing roller via the belt and forms a nip N with the belt. It has a pressure roller 305 as a.

The belt 301 has thermal conductivity and heat resistance, and has a thin cylindrical shape. This embodiment has a three-layer structure in which a base layer, an elastic layer is formed around the outer periphery of the base layer, and a releasable layer is formed around the outer periphery of the base layer. The base layer is 80 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene/perfluoroalkoxyethylene) as a fluororesin. copolymer resin) is used. The belt 301 is stretched by a fixing roller (suspension member) 300, a heating roller 307, and a suspension roller 308. The outer diameter of the belt 301 is 150 mm. The fixing roller 300 is pressed by a pressure roller 305 with the belt 301 sandwiched therebetween. For the fixing roller 300, a metal core made of metal such as SUS, copper, or aluminum is used. In this example, hollow aluminum was used. The surface elastic layer is coated with heat-resistant silicone rubber (hardness JIS-A10 [°]) with a thickness of 20 [mm], and is further coated with PTFE (polytetrafluoroethylene) with a thickness of 20 [μm]. ing. The roller hardness of the fixing roller 300 at this time is 30 to 35 [°] in ASKER-C hardness. The outer diameter of the fixing roller 300 is, for example, 70 [mm]. The above composition is an example, and other compositions may be used as long as the surface layer has wear resistance, hardness that can sufficiently secure the width of the nip N, and heat resistance.

The heating roller 307 is a 1 mm thick SUS pipe, and a halogen heater 306 as a heat source is disposed inside the roller and can generate heat up to a predetermined temperature. Belt 301 is heated by heating roller 307.

The heating roller 307 has a center of rotation at one end or near the center, and by rotating with respect to the belt 301 generates a tension difference in the front and rear directions, thereby controlling the position of the belt 310 in the main scanning direction. Further, the heating roller 307 is biased by a spring supported by a heating unit frame (not shown), and is also a tension roller that applies a predetermined tension to the belt 301.

The pressure roller 305 is a roller having a metal core layer 305c, an elastic layer on the outer periphery of the shaft, and a release layer on the outer periphery. The shaft is made of SUS material with a diameter of 72 mm, the elastic layer is made of conductive silicone rubber with a thickness of 8 mm, and the release layer is made of PFA (tetrafluoroethylene/perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm. I am using it. The pressure roller 305 is axially supported by a fixing frame (not shown) of the fixing device F, has a gear fixed to one end thereof, is connected to a drive source (not shown) via the gear, and is driven to rotate. .

In the nip N formed between the belt 301 and the pressure roller 305, the recording material P carrying the toner image is held between the belts 301 and the pressure roller 305, and the toner images are heated while being conveyed. In this way, the fixing device F fixes the toner image onto the recording material P while nipping and conveying the recording material P. A pressure roller 305 is pressed against the fixing roller 300 via the belt 301 by a drive source (not shown). The pressing force (NF) in the nip N when fixing the toner image on the recording material was 1600 N, and the width of the nip N in the X direction (conveyance direction) was set to 20 mm, and the width in the Y direction (paper width direction) was set to 336 mm. .

The purpose of the suspension roller 308 is to ensure that the fixing belt 301 has a sufficient length. Another purpose is to provide tension to the fixing belt 301. This suppresses the occurrence of wrinkles on the recording material. The suspension roller 308 is a hollow pipe made of SUS with a thickness of 1 mm, and rotates as a result of the belt.

Suspension roller 308 is disposed upstream of the nip portion in the rotational direction of fixing belt 301, contacts the inner peripheral surface of fixing belt 301, and presses the fixing belt from the inside to the outside. The fixing belt 301 is suspended by a plurality of members including a fixing roller 300 which is a suspension member. Suspension roller 308 is arranged adjacent to fixing roller 301 . Adjacent here means that there is no member that suspends the fixing belt 301 between the fixing roller 300 and the suspension roller 308.

The surface roughness was relatively smooth with arithmetic mean roughness Ra = 0.05 [μm], but if the driving torque of the belt and the scraping of the inner surface are not a problem, the surface roughness of the suspended roller There is no problem even if it is large, and the surface may be formed of a rubber member, for example.

<Mechanism of paper wrinkles>
Here, the mechanism by which paper wrinkles as shown in FIG. 6 occur will be explained.

FIG. 5 is an explanatory diagram of the mechanism by which paper wrinkles occur.

When the image forming apparatus is started up after being powered on, the end portions of the pressure roller 305 in the roller width direction (direction perpendicular to the conveying direction of the recording material) radiate heat more easily than the center portion. As a result, the temperature at the center becomes higher than that at the ends, resulting in a crown shape in which the outer diameter of the center is larger than the outer diameter of the ends.

When the recording material is conveyed with the pressure roller 305 deformed into the crown shape in this manner, the feed speed Vc at the center portion becomes faster than the feed speed Ve at the end portions. The length of the arrow representing the feed speed represents the speed of the feed speed, with the center being faster and the ends being slower. This difference in feeding speed causes distortion (distortion in which the edges move inward) in the center of the latter half of the recording material. As a result, paper wrinkles 602 as shown in FIG. 6 are likely to occur.

Therefore, the fixing device according to the present embodiment suppresses wrinkles that occur on the recording material by suppressing the difference in conveyance speed of the recording material in the width direction within the fixing nip. Details of the invention are described below.

<Shape of suspended roller>
In this embodiment, the suspension roller 308 that suspends the fixing belt 301 has an inverted crown shape. That is, in the width direction, the outer diameter of the central portion of the suspension roller 308 in the recording material passing area is made smaller than that of both ends. As a result, in the fixing belt 301 that has passed through the suspension roller 308, higher stress is generated at both ends than at the center in the width direction. Then, the conveyance speed at both ends of the fixing belt 301 is faster than at the center. As a result, it is possible to suppress paper wrinkles that conventionally occur because the center of the recording material is faster than both ends within the fixing nip. The shape of the suspension roller 308 and details of the fixing belt 301 will be described below.

The table below shows the details of the suspended rollers used in the verification.

There are multiple samples of suspended rollers 308 used for verification. The conventional example has a straight shape with a diameter of 20.0 mm (the outer diameter of the center part and the end part are the same). In order to verify the effects of this embodiment, Example 1 was used in which the center part had a diameter of 19.8 mm and both ends had a diameter of 20.0 mm (one side recessed 100 μm). Further, as Comparative Examples 1 and 3, one side recess of 50 μm and one side recess of 300 μm were used, respectively. Furthermore, as Comparative Example 2, a suspension roller was fixed and tested in a configuration in which it rubbed against the belt surface without rotating.

Further, the shape between the center and the end of the member may be in a continuous monotonous increasing or decreasing relationship with the center being the minimum, or may be connected by a straight line if there is no corner. Considering stabilization of belt running, it is ideal to connect smoothly in an arc shape like the outer diameter shape of the roller member shown in FIG. The central portion refers to the center in the width direction in the paper passing area of the recording material. Further, the end portion refers to the end portion in the width direction in the paper passing area of the recording material. Therefore, the shape of the recording material outside the paper passing area does not matter.

By forming the central portion of the suspension roller 308 shown in FIG. 7 into a concave shape, the fixing belt 301 is conveyed while being pulled in a direction extending outward within the nip after being introduced into the fixing nip portion N. By conveying the recording material following the fixing belt, the recording material is conveyed so as to be pulled outward as shown by the arrow line in FIG. 7, and the occurrence of paper wrinkles can be prevented.

<Study experiment 1>
The effect of this embodiment was verified in the fixing device configuration in Example 1.

First, we will explain the verification using actual paper.

Oji Paper OK Top Coat + 79.1 g Width 330 mm x Length 483 mm Continuous paper feeding on both sides was performed with settings to form a 100% black monochromatic image on the entire surface (320 mm width) on the T-th sheet. The output images were checked and the presence or absence of uneven gloss and paper wrinkles was recorded (Table 8).

In this example, a plurality of levels of concavity of the suspended roller were prepared, and as a comparative example, the difference in effect from Example 1 was confirmed. The results are shown in the table of FIG. 8, and it was confirmed that in this example, the paper wrinkles that occurred in the conventional example could be eliminated. Furthermore, if the amount of concavity of the suspension roller is made too large, the difference in conveyance speed is excessively reversed, and uneven gloss may occur due to poor conveyance at the edge of the paper.

Furthermore, it was confirmed that even if the suspension roller is a fixed member, if a concave shape is formed in the center, an effect of preventing paper wrinkles can be obtained. If it is a fixed member, the contact surface with the belt is configured to slide, so the durability life is disadvantageous, but it is useful depending on the configuration.

To verify the effect, a means to measure the paper transport speed at the center and the paper transport speed at the edge may be considered. Prepare a strip of paper with multiple cuts in the width direction, and place position markings on the surface of the paper. By measuring the time at the same strip position at the point where it enters the nip and the point where it leaves the nip, and plotting the speed of the paper passing through the nip in the longitudinal direction, we can calculate the absolute value of the conveyance speed at the center and edge. The difference can be measured. If this difference in conveyance speed increases to a value that cannot be tolerated due to the stiffness of the paper, wrinkles and uneven gloss will occur.
Center conveyance speed × n < Edge conveyance speed ≦ Center conveyance speed (n is a coefficient less than 1, and is variable depending on the stiffness of the paper in the CD direction. When the Gurley stiffness is 0.30 [mN], n≒0.99. do.)
The paper conveyance speed is optimized to satisfy these relationships.

Next, verification using simulation will be explained.

Simulation calculations of paper behavior in the configuration of the conventional example and the configuration of Example 1 were performed. FIG. 9 is a graph estimating the magnitude of tension (force generated in the fixing belt 301 from the center toward the outside), which is the force of the suspension roller 308 pushing the fixing belt 301. In this example, since this distance is about 50 mm, it can be seen that the concavity of the suspended roller is effective at a portion of 100 μm. If the tension is too weak, the conveyance control speed in the central portion remains slow, resulting in a state in which paper wrinkles are likely to occur due to paper deformation. If the tension is too strong, the conveyance speed at the center will be significantly slower than the conveyance speed at the edges, and uneven gloss will occur due to minute slips due to stress on the edge sides. In this way, paper wrinkles can be eliminated by making the paper concave, but by setting the concave shape of the suspension roller within an appropriate range, it is possible to further stabilize the paper conveyance speed and prevent uneven gloss. can.

As shown in FIG. 9, a good conveyance area is determined according to the tension of the suspension roller 308. Specifically, the tension is in the range of 50N or more and 100N or less. If the tension is less than 50N, the speed at the center of the recording material in the width direction will be higher than at the edges, and there is a risk that wrinkles will occur. This is because the tension applied to the fixing belt 301 is small and the speed at the edges of the recording material in the width direction cannot be made sufficiently faster than at the center. On the other hand, if the tension is greater than 100 N, the speed of the edge of the recording material in the width direction becomes too high, resulting in wrinkles. In this embodiment, a tension range of 50N to 100N is suitable. Therefore, by using the suspension roller 308 whose outer diameter is larger at both ends in the range of 50 μm or more and 300 μm or less than the center portion, wrinkles in the recording material can be suppressed by keeping the tension within a predetermined range. can.

In addition, in this embodiment, verification was performed using the suspension roller 308 of Example 1, Comparative Example 1, and Comparative Example 3, and as shown in FIG. The relationship between distance and tension changes. Specifically, the distance between the fixing nip N and the suspension roller 308 is the distance from the downstream end of the contact area between the suspension roller 308 and the fixing belt 301 to the upstream end of the fixing nip N in the rotation direction of the fixing belt 301. It is distance. When the distance between the fixing nip N and the suspension roller 308 is the same, the tension increases as the amount of crown increases. In this embodiment, if the distance between the fixing nip N and the suspension roller 308 is within the range of 25 mm or more and 110 mm or less, the tension falls within 50 N to 100 N, although it depends on the amount of crown.

FIG. 10 shows the paper shape profile before and after nip N in this simulation. In the conventional example, large undulations occurred in the front and back where the paper was deformed due to stress, but in this example, it can be visualized that the paper is being conveyed stably.

Not limited to the conditions of this embodiment, if the member immediately upstream of the nip has a concave shape, it is effective to prevent wrinkles. Preferably, the shorter the distance between the suspended roller and the nip N, and the greater the Young's modulus of the belt, the more likely the effect will appear.

The shape of the crown of the suspended roller 308 varies depending on the nip width N and the rigidity of the belt (Young's modulus of the base layer). If the nip width N is small, the distance by which the recording material is pulled outward becomes small, so the amount by which paper wrinkles are corrected decreases, and paper wrinkles may occur. Therefore, if the nip width is small, it is necessary to increase the crown amount of the suspended roller. On the other hand, if the nip width is large, the opposite is true. If the rigidity (hardness) of the belt 301 is high, it becomes difficult for the belt to follow the shape of the pad, and the amount by which the belt extends outward becomes small. This makes it difficult for the recording material to be pulled outward, resulting in paper wrinkles. Therefore, if the belt has high rigidity, it is necessary to increase the amount of crown of the suspended roller. The opposite is true if the belt has low stiffness.

As explained above, the optimum value of the crown amount D [mm] of the suspended roller 308 depends on the nip width N [mm] and the rigidity (Young's modulus [GPa]) of the base material of the belt 301, and is shown in Table 2 below. Become.

For the optimum value of the crown amount of the pad in Table 1, a simplified value calculated using ABAQUS, which is a structural calculation finite element method analysis software, was used.

The simulation conditions are as follows.
Fixing belt Outer diameter 150 mm, elastic layer thickness 300 μm, elastic layer Young's modulus 0.4 Mpa, base material thickness 80 μm, base material Young's modulus 5 Gpa
Pressure roller outer diameter φ80mm, elastic layer thickness 8mm, elastic layer Young's modulus 0.6Mpa,
Total load 80-160kgf, rotation speed 450mm/s
Using regression analysis under these conditions, the relationship between nip width [mm] and Young's modulus [GPa] can be expressed relatively simply by a linear equation,
Amount of recess of suspended roller: D [μm]
Fixing nip width: N [mm]
Belt Young's modulus: E [GPa]
The relational expression between can be expressed as follows.
D = -10xN -9.5xE +440
This is a relational expression for the combination of configurations in this embodiment, and although the numerical value may vary depending on a plurality of peripheral parameters, the magnitude relationship and approximate value of the values are correct.

Considering the range of the suspension roller concavity that can eliminate wrinkles with respect to the optimum value, there is a tolerance range of ±100 [μm] for the wrinkle elimination effect in the simulation based on the crown amount.
-10×N -9.5×E+340 <D
D < -10xN -9.5xE +540
If the recess amount D [μm] is determined within these relationships, the effects of this embodiment can be obtained.

In this embodiment, the shape of the suspension roller 308 is made larger at both ends in the width direction than at the center. This allows the conveyance speed at both ends of the fixing belt 301 to be faster than at the center. However, if the fixing belt 301 is continuously rotated, the conveying speed at both ends of the fixing belt 301 will be too faster than at the center, which may cause the fixing belt 301 to wave. Therefore, a heating roller 307 may be used in which the outer diameter of the center portion is larger than that of the end portions in the width direction. The outer diameter of the fixing roller 300 may be modified. However, if the outer diameter of the fixing roller 300, which is a member forming the nip portion N, is changed, the pressure distribution within the nip portion N may change, which is not preferable. Therefore, if the purpose is to stabilize the conveyance speed in the width direction of the fixing belt 301, it is preferable to modify the outer diameters of the heating roller 307 and the suspension roller 308.

<Example 2>
Next, the configuration of the fixing device F in the form of the second embodiment will be explained using FIG. 3.

FIG. 2 shows a schematic diagram of the overall configuration of a belt heating type fixing device F according to this embodiment. In the figure, the X direction indicates the conveying direction of the recording material P (not shown in the figure), the Y direction indicates the paper width direction, and the Z direction indicates the pressing direction. The dotted line portion represents an enlarged cross section of the nip portion N.

The fixing device F has a fixing belt (hereinafter referred to as belt) 301 as an endless rotatable heating rotating body. Further, the fixing device F includes a pressure pad (hereinafter referred to as a pad) 303 for supporting the fixing belt, a stay 302 for supporting the pad 303, and a sliding member 304 arranged to cover the pressure pad 303. The fixing belt 301 is suspended by a heating roller 307 and a suspension roller 308, and includes a pressure roller 305 as a pressure rotating body that forms a nip portion N together with the fixing belt 301.

The belt 301 has thermal conductivity and heat resistance, and has a thin cylindrical shape. This embodiment has a three-layer structure in which a base layer 301a, an elastic layer 301b is formed around the outer periphery of the base layer 301a, and a releasable layer 301c is formed around the outer periphery of the base layer 301a. The base layer is 80 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene/perfluoroalkoxyethylene) as a fluororesin. copolymer resin) is used. The belt 301 is stretched by a pad 303, a heating roller 307, and a suspension roller 308. The outer diameter of the belt 301 is 150 mm.

Pad 303 is pressed by pressure roller 305 with belt 301 in between. The pad 303 is made of LCP (liquid crystal polymer) resin. A sliding member 304 is interposed between the pad 303 and the belt 301. An embossed portion was formed on the surface layer of the sliding member 304, and was coated with PTFE (polytetrafluoroethylene) with a thickness of 20 μm to achieve low friction. By further applying lubricant to the inner surface of the belt 301, the belt 301 is configured to slide smoothly on the sliding member 304. Silicone oil was used as the above lubricant. A stay 302 was used to supplement the strength of the pad 303.

The sliding member 304 of this embodiment is configured to cover the pad 303 regardless of whether it is inside or outside the nip portion N. Although not shown hereafter, it does not matter if a part of the nip N is covered with the sliding member 304. That is, a configuration in which the sliding member 304 is disposed only in the nip portion N may be used.

The heating roller 307 is a stainless steel pipe with a thickness of 1 mm, and a halogen heater 306 as a heat source is disposed inside the roller and can generate heat up to a predetermined temperature. Belt 301 is heated by heating roller 307.

The suspension roller 308 has a center of rotation at one end or near the center, and by rotating relative to the belt 301, generates a tension difference in the front and rear directions, thereby controlling the position of the belt 301 in the main scanning direction. Further, this suspension roller 308 is biased by a spring supported by a shift control frame (not shown) that fixes the suspension roller 308, and is also a tension roller that applies a predetermined tension to the belt 301.

The pressure roller 305 is a roller having a metal core layer 305c, an elastic layer on the outer periphery of the shaft, and a release layer on the outer periphery. The shaft is made of SUS material with a diameter of 72 mm, the elastic layer is made of conductive silicone rubber with a thickness of 8 mm, and the release layer is made of PFA (tetrafluoroethylene/perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm. I am using it. The pressure roller 305 is axially supported by a fixing frame (not shown) of the fixing device F, has a gear fixed to one end thereof, is connected to a drive source (not shown) via the gear, and is driven to rotate. .

In the nip N formed between the belt 301 and the pressure roller 305, the recording material P carrying the toner image is held between the belts 301 and the pressure roller 305, and the toner images are heated while being conveyed. In this way, the fixing device F fixes the toner image onto the recording material P while nipping and conveying the recording material P. Therefore, it is necessary to have both the function of applying heat and pressure and the function of conveying the recording material P. A pressure roller 305 is pressed against the pad 303 via the belt 301 by a drive source (not shown). The pressing force (NF) in the nip N during printing was 1600 N, and the width of the nip N in the X direction (conveyance direction) was set to 24.5 mm, and the width in the Y direction (paper width direction) was set to 336 mm.

<Study experiment 2>
In the fixing device configuration in Example 2, the effects of this embodiment were verified, but the results were almost the same as in Example 1, with the relationship shown in FIG. 8, so the explanation will be omitted.

The parameter values in the corresponding simulations are also the same, so even if the upstream member changes, as long as the concave shape relationship is the same, the effect of regulating the belt will be the same, and the effect of preventing paper wrinkles will be achieved. can.

F Fixing device N Nip section 300 Fixing roller (suspension member)
301 Fixing belt 302 Stay 303 Pressure pad (pad)
304 Sliding member 305 Pressure roller 306 Halogen heater 307 Heating roller 308 Suspension roller

Claims (9)

a fixing belt that is rotatable and applies heat to the recording material;
a suspension member that comes into contact with an inner peripheral surface of the fixing belt and suspends the fixing belt;
a pressure rotating body that forms a nip portion by pressurizing the suspension member via the fixing belt;
The fixing belt and the pressure rotating body sandwich and convey a recording material carrying a toner image in the nip portion, and fix the toner image on the recording material by applying heat and pressure to the recording material;
a suspension roller that suspends the fixing belt upstream of the nip portion in the rotational direction of the fixing belt;
The suspension roller is adjacent to the suspension member among the plurality of members suspending the fixing belt,
In the width direction of the suspension roller, the center of the paper passing area of the recording material is the center part, and both ends of the paper passing area are both ends,
The fixing device according to claim 1, wherein the outer diameter of the suspension roller is larger in the range of 50 μm or more and 300 μm or less at both end portions than at the center portion. The fixing device according to claim 1, wherein a distance between the nip portion and the suspension roller is 25 mm or more and 110 mm or less. The fixing device according to claim 1, wherein the force with which the suspension roller pushes the fixing belt from the inside to the outside of the fixing belt is 50 N or more and 100 N or less. The fixing device according to claim 1, wherein the suspension roller rotates following rotation of the fixing belt. 2. The fixing device according to claim 1, wherein the central portion has the smallest outer diameter in the paper passing area. The fixing device according to claim 5, wherein the outer diameter increases along the width direction from the center portion to the both end portions. The fixing device according to claim 1, further comprising a rotatable heating roller having a heat source downstream of the nip portion in the rotation direction. 8. The fixing device according to claim 7, wherein in the width direction, the outer diameter of the heating roller is smaller at both ends of the paper passing area than at the center of the paper passing area. The fixing device according to claim 1, wherein the suspension member is a rotatable fixing roller, and the fixing roller has an elastic layer.

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